1. Field of the Invention
The present invention is in the field of communication systems and specifically relates to a virtual hold technique and a self-testing technique for use in such systems.
2. The Prior Art
In U.S. Pat. No. 4,176,254, Tuttle, et al. show a solar powered call box system that is capable of transmitting voice and data. The system includes a plurality of emergency switches marked with symbols corresponding to various emergency conditions.
Cannalte, et al., in U.S. Pat. No. 3,939,417 show a system in which, if the primary channel is busy, a second caller is switched to a second channel. When the first call is completed, the second call is connected to the primary channel. The console operator can interrogate any of the call boxes to determine their status.
In U.S. Pat. No. 4,406,995, May shows an improved method and apparatus by which a base station can monitor the state of several functions in a call box.
The above-described patents are the most relevant ones known in regard to the virtual hold features of the present invention, and the patents mentioned in the following paragraphs are the known patents that are closest to the self-testing feature of the present invention.
In U.S. Pat. No. 3,598,929, Seldman describes a test instrument capable of being carried into the field by a repairman, and that provides a standardized acoustic source, a standardized audio frequency oscillator, and an audio frequency voltmeter. Using these items, the repairman can determine whether the microphone or the speaker of the telephone instrument is defective and whether the loop between the instrument and the central office is defective. A comparable instrument is described in U.S. Pat. No. 3,261,926 to Bryant, et al.
In U.S. Pat. No. 4,037,222 issued in 1977 to Solomon, there is shown a system for supervising a number of loudspeakers to determine whether they are operating. A transducer is mounted on and sensitive to vibrations of a speaker cone to produce a signal that indicates whether the speaker is operating. This signal is fed back to the central office on a separate supervisory wire, or on the same wires that power the speakers, but in a different frequency band.
Although the above patents show that much work has been done in the general field of call boxes, none of the patents describes or suggests the specific features that will be described below.